1. Field of the Invention
The present invention relates to a receiving apparatus for a mobile terminal, and more particularly to an apparatus and a method for branching signals received by a mobile terminal in different communication bands.
2. Background of the Related Art
FIG. 1 is a block diagram showing a general CDMA mobile terminal, which includes an antenna 10, a radio frequency (RF) unit 20, an intermediate frequency (IF) unit 30, a baseband analog (BBA) unit 40, a baseband modem 50, and an input/output unit 60. The RF unit 20 converts a high frequency signal to an intermediate frequency signal of a modulated carrier, and the IF unit 30 converts the intermediate frequency signal to a baseband frequency signal. The BBA unit 40 converts an analog signal output from the IF unit to a baseband digital signal. The baseband modem 50 controls an input/output signal of a display panel included in input/output unit 60 and of a keypad. The baseband modem further controls voice input/output on a microphone and an earphone.
FIG. 2 is a block diagram showing the structure of RF unit 20 of the CDMA mobile terminal. As shown, when an RF signal is received from an outer part, a received frequency signal is separated from the RF signal input from antenna 10 by a duplexer 21. The received frequency signal is then amplified by a low noise amplifier (LNA) 26 and converted into an intermediate frequency signal by a down-conversion mixer (DMIX) 28 after passing through a band pass filter 27. The converted intermediate signal is amplified in an IF amplifier 29 and sent to the IF unit 30.
In a transmission process, an intermediate frequency signal output from the IF unit 30 is converted into an RF signal by an up-conversion mixer (UMIX) 25. This signal is then amplified by a driver amplifier 23 after passing through a band pass filter 24, and the power of the signal output from the driver amplifier is amplified by a power amplifier 22. The resulting signal is sent to a base station through the antenna.
CDMA mobile terminals of the aforementioned type have been adapted to perform a function of satellite-based global positioning system (GPS). Terminals of this type support one or more bands including an 800 MHz DCN band, a Korea-type 1.8 GHz PCS band, a U.S. type 1.9 GHz PCS band, and 1.5 GHz GPS band. That is, the CDMA mobile terminal which performs the GPS function is divided into a dual-band terminal which operates in DCN and GPS bands or PCS and GPS bands and a tri-band terminal which operates in DCN, PCS and GPS bands.
FIG. 3 shows a conventional receiving apparatus of a mobile terminal using a single antenna supporting the tri-band, and FIG. 4 shows a conventional receiving apparatus of a mobile terminal using a dual-band antenna and a single band antenna. As shown therein, since the mobile terminal is operated in one or more bands, a circuit for branching an RF signal by respective bands is required in the antenna supporting the multi-bands. For example, in case of a U.S. type tri-band terminal having the most complex configuration, one antenna 70 supporting the tri-band of DCN, PCS and GPS may be used, or a dual band antenna supporting the DCN and PCS and single band antenna 90 supporting only the GPS may be used respectively.
The single antenna supporting the tri-band of DCN, PCS and GPS as shown in FIG. 3 will now be described in greater detail. An RF signal received by the tri-band antenna 70 is branched to a duplexer of DCN band 75 and to another diplexer of GPS and PCS band 72 by a diplexer 71. After that, the diplexer 72 transmits the input signal to an RF band pass filter 73 of GPS band when the input signal is in 1.5 GHz band, and transmits the input signal to a PCS duplexer 74 of PCS band when the input signal is in 1.9 GHz band. That is, diplexers 71 and 72 are a kind of manual filter made by integrating two band pass filters. Functionally, diplexer 71 outputs an input signal from antenna 70 to an input stage of a DCN transceiver if the input signal is in the 800 MHz band, and outputs through diplexer 72 the input signal to an input stage of a GPS or PCS transceiver if the input signal is in the 1.5 to 1.8 GHz band.
The dual-band antenna supporting the DCN and PCS bands and the single-band antenna 90 supporting the GPS band shown in FIG. 4 will now be described in greater detail. The RF signal received by the dual band antenna 80 is branched to a PCS diplexer 83 when it is in the PCS band, and to a DCN duplexer 82 when it is in the DCN band after passing diplexer 81. In addition, the GPS signal is received by additional antenna 90 of the GPS band and input into an RF band pass filter 91.
Diplexers 71, 72 and 81 for branching the signal in the mobile terminal are undesirable because they have an insertion loss (e.g., a loss when the signal is passed) of 0.5˜0.8 dB, and have an isolation corresponding to the isolated degree between bands of 15˜20 dB. The insertion loss is generated as a result of signals passing through two or more diplexers in order to branch the multi-band signal, and therefore receiver sensitivity is lowered. For example, insertion loss can be increased to 1˜1.5 dB in case that the two diplexers 71 and 72 in FIG. 3 are used. Also, in case of the GPS having isolation between bands as an important factor, isolation of about 15˜20 dB can be too weak to block the interrupt between the different bands.